Portable engine-operated implements such as lawn mowers, chainsaws, hedge clippers, etc. are the cause of many injuries in or about the home. The problem of consumer injury is so severe that consumer safety agencies have enacted safety standards relating to their design.
The most common source of injury is a rotating or reciprocating implement blade. Often, the blades are exposed while in operation or are accessible while in an "idle" condition. One possible safety measure is to provide a braking means for holding the implement blade against motion during an "idle" condition or other standby or nonuse condition. Incorporating a braking system into a portable implement, such as a gasoline powered lawnmower, would diminish the likelihood of severing the implement operator's fingers by accidental contact with an implement blade. Such accidents often happen when the implement is turned off after use and the implement blade is coasting due to blade momentum. The portable engine-operated implement industry has sought such a braking means for portable engine-operated implements. Several braking systems have been developed, all of which have serious shortcomings.
One braking system uses a manual brake. In this system, the engine is started; the operator assumes an operating position with the implement; and a deadman switch is engaged by the operator. The implement clutch is then mechanically engaged with the implement tool and the implement tool is driven by the engine. When the operator releases the "deadman switch", the clutch mechanically disengages the engine from the implement tool, which allows it to brake to a stop. Among the disadvantages of such a system are: (1) the "deadman switch" is easily disabled by using tape, rope or wire to hold it in place; (2) the clutch mechanism is subject to damage by entry of foreign matter during operation; (3) the system is hard to maintain and requires highly trained, certified personnel as well as special tools and equipment; and (4) the clutch is usually stiff, requiring a tiring amount of operator control to keep the "deadman switch"engaged during implement operation.
Another approach to solving the problem of implement tool control is the "engine stop" system. The "engine stop" includes an electric starter for starting the engine, a "deadman switch", and a complicated electrical control system for sensing blade motion. The "deadman switch" terminates operation of the engine to stop implement tool motion each time the "deadman switch" is released by the operator. Among the disadvantages of the "engine stop" approach are: (1) the system requires an expensive and elaborate electrical and mechanical arrangement to start the engine including batteries and a starter motor; (2) it necessitates constant restarting of the engine; (3) the system requires regular and repeated adjustment to keep it in proper operating condition; (4) the resistance of the implement tool to movement on an operating surface is so great that the implement engine often cannot obtain enough speed to start; and (5) the system is easily bypassed to disable the "deadman switch".
A further shortcoming of the "engine stop" system is that the implement tool is active (moving) during startup of the implement engine. This can result in operator injury from inadvertently starting the engine while the operator's hands are near the implement blades.
The present system eliminates the excessive manual control required to engage the clutch, eliminates the complicated and expensive electrical system with its electric starter and battery, eliminates the possibility of malfunction due to contamination by foreign debris, eliminates the possibility of tampering to disable the system, and simplifies maintenance for servicing personnel. It makes tool engagement below operating speeds at start up impossible. It prevents tool coasting.
The system uses a sealed electrically operated clutch unit to keep out dirt and debris. Such a clutch unit is more reliable than the open-access mechanical clutches. The electrical clutch is also more positive in operation than the mechanical clutch. It requires less operator pressure on a "Deadman Switch" to operate than does a mechanical clutch.